Chain Heteroatom Research Articles

Discerning Emittable from Extractable Chemicals Identified in Consumer Products by Suspect Screening GCxGC-TOFMS.

Characterization of chemicals in household products is important for understanding this potential source of chemical exposure. Increasingly, suspect screening and nontargeted analysis techniques are used to characterize as many chemical signatures as possible. Solids such as household products are most conveniently prepared using solvent extraction, revealing what chemicals are contained within the product matrix but providing no information about the potential of those chemicals to leave the matrix and cause actual exposure. In this work, the profile and relative abundances of "extractable" chemical signatures found after solvent extraction are compared to those "emittable" to the headspace for 81 household products analyzed by two-dimensional gas chromatography time-of-flight mass spectrometry. This study retrospectively fuses data collected in separate efforts over 3.8 years and 13 analytical batches. Management of the data is made possible by recent developments in processing systems for complex data such as Highlight. Compounds were generically classified as aromatic heteroatom, aromatic hydrocarbon, glycol, hydrocarbon, long chain heteroatom, nonaromatic heteroatom, and unknown/unclassified. Class-based retention time and abundance trends were observed. Liquid extraction resulted in the greatest number of features and the highest relative abundances, while low temperature emission conditions produced the smallest number of features and lowest relative abundances.

English

Good environmental stability, High degree of processability and interesting redox properties associated with its chain heteroatom, polyaniline (PANI) has been one of the most extensively studied conducting polymers during the past ten years. The present review attempts for the first time to summarize the explicit and quantitative dealings with the various intrinsic oxidation states of PANI and its synthesis, Characterizations, Development and applications of polyaniline derivatives that have been made during the past decade. The paper includes the advantages of some selected studies carried out on polyaniline and polyaniline Nobel metal composites and the superiority of Polyaniline. Details are provided of the different methods used for the synthesis of PANI along with mechanisms, theoretical studies and number of special methods used to obtain a nanostructured PANI. A detailed discussion on the mechanism of electrical conduction in PANI and the factors those influence the conductivity of PANI is also included. Finally, the progress towards technological applications is evaluated.

Synthesis, optical properties and lamellar self-organization of new N,N′,N″-trialkyl-triazatriangulenium tetrafluoroborate salts

Here we report the synthesis of six new N,N′,N″-trialkyl-triazatriangulenium (R3-TATA+) tetrafluoroborate salts with ether functions in their side chains. Solution and solid-state optical properties of the R3-TATA+ salts were investigated to elucidate the influence of the side chain heteroatoms on the electronic structure of the chromophore. Structural studies of spin-cast thin films of nine different R3-TATA+ BF4− salts showed, for all derivatives, formation of a rare structure with homeotropic aligned discotic dyes in a lamellar structure. In the lamellar structure, layers of the charged discotic TATA+ dyes and their counter ions are separated by the perpendicularly oriented alkyl chains. In all cases, it was found that simple spin-casting gave films with macroscopic alignment of the lamellar structure parallel to the substrate. Formation of the lamellar structure, for all the R3-TATA+ BF4− salts, both with branched and linear side chains, highlight the robustness of this self-organizing motif.

The role of proton bridges in selective cleavage of Ser-, Thr-, Cys-, Met-, Asp-, and Asn-containing peptides

Fragmentation patterns of doubly charged peptides containing serine (Ser), threonine (Thr), cysteine (Cys), homoserine (Hse), methionine (Met), aspartic acid (Asp), or asparagine (Asn) and terminating with arginine (Arg) were investigated. Stronger cleavages N-terminal to Ser, Thr, Cys, Asp, and Asn were observed in comparison to their C-terminal cleavages. In contrast, stronger cleavages C-terminal to Hse and Met were observed compared to their N-terminal cleavages. These fragmentation patterns can be explained by the relative stabilities of intramolecular proton bridges that form between the side chain heteroatoms (hydroxyl oxygen, carbonyl oxygen or sulfur) and the neighboring backbone carbonyl oxygens. Literature data and results from molecular dynamics are used to explain the stabilities of the proton bridges with different ring sizes based on the site of the bridge. For Ser, Thr, Cys, Asn and Asp, the proton bridge between the side chain and the adjacent N-terminal carbonyl is more stable and thus favored over the one to the adjacent C-terminal carbonyl, resulting in N-terminal enhanced cleavage. For Met and Hse, the proton bridge between the side chain and the C-terminal carbonyl is more stable, leading to C-terminal enhanced cleavages.

Synthesis and NMR assignment of pentacycloundecane precursors of potential pharmaceutical agents

The synthesis and complete NMR elucidation of eight novel pentacycloundecane (PCU) derivatives are reported. These compounds are precursors in the synthesis of PCU-based anti-tuberculosis (TB) agents and potential human immunodeficiency virus (HIV) protease inhibitors. Two-dimensional (2D) NMR techniques were used to assign the NMR spectra for these compounds. Substitution of the cage molecule at (C-8/11) further complicates the assignment, since some of the substituted alkyl chain groups overlap with the cage proton signals. The side chain heteroatoms also introduce a rare through-space deshielding effect to some of the carbon atoms of the cage skeleton. Ring strain in the rigid cage skeleton appears to induce drastic electronic changes in some parts of the cage framework. This observation is more dramatic for the C-4 methylene group of the cage diols and the cage ethers.

Acyl transfer from carboxylate, carbonate, and thiocarbonate esters to enzymatic and nonenzymatic thiolates

Transglutaminases (EC 2.3.2.13) (TGases) catalyze calcium-dependent acyl transfer reactions between peptide-bound glutamine residues as acyl donors and peptide-bound lysine residues as acyl acceptors, resulting in the formation of intermolecular ε-(γ-glutamyl)lysine crosslinks. The mechanistic details of its "ping-pong" transamidation reaction remain unknown. In particular, few studies have been published probing the nucleophilicity of TGase using acyl-donor substrates of varied electrophilicity. Herein we report the synthesis of activated esters of carbonates, carbamates, and thiocarbonates and their reactions with simple thiols, as a nonenzymatic point of reference, and with the catalytic cysteine residue of guinea pig liver TGase. Our kinetic results show that the simple substitution of a side chain methylene unit by oxygen or sulphur had a surprising effect on both substrate affinity and acylation reactivity. Furthermore, they provide unexpected insight into the importance of a side chain heteroatom for conferring affinity for tissue TGase as well as revealing an interesting class of irreversible inhibitors.Key words: enzyme kinetics, enzyme inhibition, transglutaminase, acyl-transfer reactions, carbamate, thiocarbonate, carbonate.

Molecular recognition of modified adenine nucleotides by the P2Y(1)-receptor. 2. A computational approach.

The molecular recognition of C2- or C8-substituted ATP derivatives by the P2Y(1)-receptor (P2Y(1)-R) is analyzed using ab initio quantum mechanical calculations. Parameters that may determine ligand specificity toward P2Y(1)-R were examined on reduced models and correlated with the biochemical data for the parent compounds. These include tautomerism and protonation energy in the gas and aqueous phases, as well as molecular electrostatic potential (MEP) and dipole moment vector. The calculated electronic parameters cannot explain the inactivity of the C8-substituted ATP derivatives, nor the difference in activity among the C2-substituted ATP analogues. These results indicate that neither tautomerism nor changes in the electronic distribution of the adenine ring play a major role in determining binding specificity of adenine nucleotides to the receptor. It is suggested that the higher potency of the C2-substituted ATP derivatives, compared to ATP, might be due to interaction between the C2 side chain heteroatom and the receptor. Furthermore, the interaction of the C2 alkyl side chain with a hydrophobic pocket at the receptor binding site is suggested. In addition, NMR data in the companion paper indicate that the inactivity of the C8-substituted ATP analogues may be due to steric and conformational, rather than electronic, effects.

Synthesis, Characterization, and Optical Properties of Inorganic Polymer Films

ABSTRACTThe linear and non-linear optical response of phosphazene and siloxane polymers and cyclic precursors is influenced by the nature of chemical groups substituted onto the heteronuclear backbone chains. Polymer mechanical properties, chemical stability, and solubility also are affected. Significant variations in both second and third order susceptibilities have been measured for various substituted phosphazene materials. The electron donating tendency of substitutional groups appears to correlate with the measured non-linear optical properties determined by SHG and DFWM experiments in these systems where d¦-p¦ bonding along the polymer chain is important. Approaches to the synthesis, and deposition of these materials as thin films will be discussed. Variations in optical properties are highlighted for several model systems in terms of substitutional group perturbation to the chemical bonding between the chain heteroatoms.